Optical imaging system

ABSTRACT

An optical imaging system includes a first lens having a concave image-side surface, a second lens having a concave image-side surface, and a third lens having a positive refractive power. The optical imaging system includes a fourth lens having a positive refractive power and a concave object-side surface, a fifth lens, a sixth lens having a positive refractive power, and a seventh lens having a concave object-side surface. The first lens to the seventh lens are sequentially disposed at intervals from an object side toward an imaging plane.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation Application of U.S. patentapplication Ser. No. 15/445,125, filed on Feb. 28, 2017, which claimsthe benefit under 35 U.S.C. § 119(a) of Korean Patent Application No.10-2016-0159263 filed on Nov. 28, 2016, in the Korean IntellectualProperty Office, the entire disclosures of which are incorporated hereinby reference for all purposes.

BACKGROUND 1. Field

The following description relates to an optical imaging system includingseven lenses.

2. Description of Related Art

As the degree of resolution of small cameras has continued to improve,pixels included in image sensors have become smaller. For example, animage sensor of a camera having a resolution of 13 megapixels or moremay have a pixel size smaller than that of an image sensor of aneight-megapixel camera. As the phenomenon described above involves areduction in an amount of light incident on each pixel of an imagesensor, it may be difficult to obtain a clear and bright image.Therefore, optical imaging systems for improving resolution andbrightness are being developed.

SUMMARY

This Summary is provided to introduce a selection of concepts, insimplified form, that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In a general aspect, an optical imaging system includes a first lenshaving a concave image-side surface, a second lens having a concaveimage-side surface, and a third lens having a positive refractive power.The optical imaging system also includes a fourth lens having a positiverefractive power and a concave object-side surface, a fifth lens, asixth lens having a positive refractive power, and a seventh lens havinga concave object-side surface. The first lens to the seventh lens aresequentially disposed at intervals from an object side toward an imagingplane.

The first lens of the optical imaging system may have a convexobject-side surface along the optical axis. The second lens of theoptical imaging system can have a convex object-side surface along theoptical axis. The third lens of the optical imaging system may have aconvex object-side surface along the optical axis and a concaveimage-side surface along the optical axis.

The fifth lens of the optical imaging system may have a concaveobject-side surface along the optical axis and a convex image-sidesurface along the optical axis. The sixth lens of the optical imagingsystem can have a convex object-side surface along the optical axis anda concave image-side surface along the optical axis. The seventh lens ofthe optical imaging system may have a concave image-side surface alongthe optical axis.

In another general aspect, an optical imaging system includes a firstlens, a second lens, a third lens, a fourth lens, a fifth lens, a sixthlens, and a seventh lens, sequentially disposed from an object sidetoward an imaging plane. The optical imaging system satisfies theconditional expression f2/f<−2.0, where f represents an overall focallength of the optical imaging system and f2 is a focal length of thesecond lens.

The optical imaging system may satisfy the conditional expression0<f1/f<2.0, where f represents an overall focal length of the opticalimaging system and f1 represents a focal length of the first lens. Theoptical imaging system can satisfy the three conditional expressions25<V1−V2<45, V1−V3<25, and 25<V1−V5<45, where V1 represents an Abbenumber of the first lens, V2 represents an Abbe number of the secondlens, V3 represents an Abbe number of the third lens, and V5 representsan Abbe number of the fifth lens.

The optical imaging system may satisfy the conditional expression1.5<f3/f, where f represents an overall focal length of the opticalimaging system and f3 represents a focal length of the third lens. Theoptical imaging system can also satisfy the conditional expression3.0<|f4/f|, where f represents an overall focal length of the opticalimaging system and f4 represents a focal length of the fourth lens. Theoptical imaging system can include concave image-side surfaces on thefirst lens and the sixth lens, as well as a concave object-side surfaceof the fourth lens.

In another general aspect, an optical imaging system includes a firstlens having a positive refractive power, a second lens having a negativerefractive power, and a third lens. The optical imaging system alsoincludes a fourth lens having a convex image-side surface along theoptical axis, a fifth lens having a negative refractive power, a sixthlens, and a seventh lens having a negative refractive power.

The optical imaging system can satisfy the conditional expression−1.3<f1/f2, where f1 represents a focal length of the first lens and f2represents the focal length of the second lens. The optical imagingsystem may satisfy the conditional expression f5/f<0, where f representsan overall focal length of the optical imaging system and f5 representsa focal length of the fifth lens. The optical imaging system can satisfythe conditional expression f7/f<0, where f represents an overall focallength of the optical imaging system and f7 represents a focal length ofthe seventh lens.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of an optical imaging system, according to a firstexample.

FIG. 2 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 1.

FIG. 3 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 1.

FIG. 4 is a view of an optical imaging system, according to a secondexample.

FIG. 5 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 4.

FIG. 6 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 4.

FIG. 7 is a view of an optical imaging system, according to a thirdexample.

FIG. 8 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 7.

FIG. 9 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 7.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements, where applicable. The drawings maynot be to scale, and the relative size, proportions, and depiction ofelements in the drawings may be exaggerated for clarity, illustration,and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of functions and constructions that are well known may beomitted for increased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided merelyto illustrate some of the many possible ways of implementing themethods, apparatuses, and/or systems described herein that will beapparent after an understanding of the disclosure of this application.

Although terms such as “first,” “second,” and “third” may be used hereinto describe various components, regions, or sections, these components,regions, or sections are not to be limited by these terms. Rather, theseterms are only used to distinguish one component, region, or sectionfrom another component, region, or section. Thus, a first component,region, or section referred to in examples described herein may also bereferred to as a second component, region, or section without departingfrom the teachings of the examples.

The terminology used herein is for describing various examples only, andis not to be used to limit the disclosure. The articles “a,” “an,” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. The terms “comprises,” “includes,”and “has” specify the presence of stated features, numbers, operations,members, elements, and/or combinations thereof, but do not preclude thepresence or addition of one or more other features, numbers, operations,members, elements, and/or combinations thereof.

Due to manufacturing techniques and/or tolerances, variations of theshapes shown in the drawings may occur. Thus, the examples describedherein are not limited to the specific shapes shown in the drawings, butinclude changes in shape that occur during manufacturing.

The features of the examples described herein may be combined in variousways as will be apparent after an understanding of the disclosure ofthis application. Further, although the examples described herein have avariety of configurations, other configurations are possible as will beapparent after an understanding of the disclosure of this application.

Examples provide optical imaging systems having a high degree ofbrightness and having high resolution for mounting in a small terminal.Hereinafter, examples are described in further detail with reference tothe accompanying drawings.

In accordance with an example, a first lens refers to a lens closest toan object or a subject from which an image is captured. A seventh lensis a lens closest to an imaging plane or an image sensor. In anembodiment, all radii of curvature of lenses, thicknesses, a distancefrom an object-side surface of a first lens to an imaging plane (OAL), ahalf diagonal length of the imaging plane (IMG HT), and focal lengths ofeach lens are indicated in millimeters (mm). A person skilled in therelevant art will appreciate that other units of measurement may beused. Further, in embodiments, all radii of curvature, thicknesses, OALs(optical axis distances from the first surface of the first lens to theimage sensor), a distance on the optical axis between the stop and theimage sensor (SLs), image heights (IMGHs) (image heights), and backfocus lengths (BFLs) of the lenses, an overall focal length of anoptical system, and a focal length of each lens are indicated inmillimeters (mm). Further, thicknesses of lenses, gaps between thelenses, OALs, TLs, SLs are distances measured based on an optical axisof the lenses.

A surface of a lens being convex means that an optical axis portion of acorresponding surface is convex, and a surface of a lens being concavemeans that an optical axis portion of a corresponding surface isconcave. Therefore, in a configuration in which one surface of a lens isdescribed as being convex, an edge portion of the lens may be concave.Likewise, in a configuration in which one surface of a lens is describedas being concave, an edge portion of the lens may be convex. In otherwords, a paraxial region of a lens may be convex, while the remainingportion of the lens outside the paraxial region is either convex,concave, or flat. Further, a paraxial region of a lens may be concave,while the remaining portion of the lens outside the paraxial region iseither convex, concave, or flat. In addition, in an embodiment,thicknesses and radii of curvatures of lenses are measured in relationto optical axes of the corresponding lenses.

In accordance with illustrative examples, the embodiments described ofthe optical system include seven lenses with a refractive power.However, the number of lenses in the optical system may vary, forexample, between two to seven lenses, while achieving the variousresults and benefits described below. Also, although each lens isdescribed with a particular refractive power, a different refractivepower for at least one of the lenses may be used to achieve the intendedresult.

An optical imaging system includes seven lenses. For example, theoptical imaging system may include a first lens, a second lens, a thirdlens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens,sequentially disposed from an object side.

The first lens has a refractive power. For example, the first lens has apositive refractive power. One surface of the first lens is concave. Inan embodiment, an image-side surface of the first lens may be concave.

The first lens may have an aspherical surface. For example, bothsurfaces of the first lens are aspherical. The first lens is formed of amaterial having a high degree of light transmissivity and excellentworkability. In an example, the first lens is formed of a plasticmaterial. However, the material of the first lens is not limited tobeing a plastic material. In another example, the first lens may beformed of a glass material. The first lens may have a low refractiveindex. In an embodiment, the refractive index of the first lens is lowerthan 1.6.

The second lens has a refractive power. For example, the second lens hasa negative refractive power. One surface of the second lens is concave.In an embodiment, an image-side surface of the second lens is concave.

The second lens has an aspherical surface. For example, an object-sidesurface of the second lens is aspherical. The second lens is formed of amaterial having a high degree of light transmissivity and excellentworkability. In an example, the second lens is formed of a plasticmaterial. However, a material of the second lens is not limited to beingplastic. In another example, the second lens may be formed of a glassmaterial. The second lens may have a refractive index higher than thatof the first lens. In an embodiment, the refractive index of the secondlens is 1.65 or higher.

The third lens has a refractive power. For example, the third lens has apositive refractive power. The third lens has an aspherical surface. Forexample, an image-side surface of the third lens is an asphericalsurface.

The third lens is formed of a material having a high degree of lighttransmissivity and excellent workability. For example, the third lens isformed of a plastic material. However, a material of the third lens isnot limited to being plastic. In another example, the third lens may beformed of a glass material. The third lens has a refractive indexsubstantially similar to that of the first lens. In an embodiment, therefractive index of the third lens is lower than 1.6.

The fourth lens has a refractive power. For example, the fourth lens hasa positive refractive power. One surface of the fourth lens is concave.In an embodiment, an object-side surface of the fourth lens is concave.

The fourth lens has an aspherical surface. For example, both surfaces ofthe fourth lens are aspherical. The fourth lens is formed of a materialhaving a high degree of light transmissivity and excellent workability.In an example, the fourth lens is formed of a plastic material. However,a material of the fourth lens is not limited to being plastic. Inanother example, the fourth lens may be formed of a glass material. Thefourth lens has a refractive index substantially the same as that of thethird lens. For example, the refractive index of the fourth lens islower than 1.6.

The fifth lens has a refractive power. For example, the fifth lens has anegative refractive power. The fifth lens includes an asphericalsurface. For example, both surfaces of the fifth lens are aspherical.

The fifth lens is formed of a material having a high degree of lighttransmissivity and excellent workability. In an example, the fifth lensis formed of a plastic material. However, a material of the fifth lensis not limited to being plastic. In another example, the fifth lens maybe formed of a glass material. The fifth lens has a refractive indexhigher than that of the first lens. For example, the refractive index ofthe fifth lens is 1.6 or higher.

The sixth lens has a refractive power. For example, the sixth lens has apositive refractive power. The sixth lens has an inflection point. In anembodiment, both surfaces of the sixth lens have one or more inflectionpoints.

The sixth lens has an aspherical surface. As an example, both surfacesof the sixth lens are aspherical. The sixth lens is formed of a materialhaving a high degree of light transmissivity and excellent workability.In an example, the sixth lens is formed of a plastic material. However,a material of the sixth lens is not limited to being plastic. In anotherexample, the sixth lens may be formed of a glass material. The sixthlens has a refractive index substantially similar to that of the fifthlens. For example, the refractive index of the sixth lens is 1.6 orhigher.

The seventh lens has a refractive power. For example, the seventh lenshas a negative refractive power. One surface of the seventh lens isconvex. In an embodiment, an object-side surface of the seventh lens isconvex. The seventh lens has an inflection point. For example, bothsurfaces of the seventh lens have one or more inflection points.

The seventh lens has an aspherical surface. For example, both surfacesof the seventh lens are aspherical. The seventh lens is formed of amaterial having a high degree of light transmissivity and excellentworkability. In an example, the seventh lens is formed of a plasticmaterial. However, a material of the seventh lens is not limited tobeing plastic. In another example, the seventh lens may be formed of aglass material. The seventh lens has a refractive index lower than thatof the sixth lens. For example, the refractive index of the seventh lensis lower than 1.6.

Aspherical surfaces of the first lens to the seventh lens may berepresented by Equation 1.

$\begin{matrix}{Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {Ar}^{4} + {Br}^{6} + {Cr}^{8} + {Dr}^{10} + {Er}^{12} + {Fr}^{14} + {Gr}^{16} + {Hr}^{18} + {Jr}^{20}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, c represents an inverse of a radius of curvature of thelens, k represents a conic constant, r represents a distance from acertain point on an aspherical surface of the lens to an optical axis, Ato J represent aspherical constants, and Z (or SAG) represents adistance between the certain point on the aspherical surface of the lensat the distance r and a tangential plane meeting the apex of theaspherical surface of the lens.

The optical imaging system further includes a filter, an image sensor,and a stop. The filter may be disposed between the seventh lens and theimage sensor. The filter may block some wavelengths of light to obtain aclear image. For example, the filter blocks infrared wavelengths oflight.

The image sensor forms an imaging plane. For example, a surface of theimage sensor forms an imaging plane. The stop is disposed to adjust anamount of light incident on a lens. In examples, the stop may bedisposed between the second lens and the third lens, or between thethird lens and the fourth lens.

The optical imaging system satisfies any one of or any combination ofany two or more of the following Conditional Expressions:

[Conditional Expression 1] 0 < f1/f < 2.0 [Conditional Expression 2] 25< V1 − V2 < 45 [Conditional Expression 3] V1 − V3 < 25 [ConditionalExpression 4] 25 < V1 − V5 < 45 [Conditional Expression 5] f2/f < −2.0[Conditional Expression 6] 1.5 < f3/f [Conditional Expression 7] 3.0 <|f4/f| [Conditional Expression 8] f5/f < 0 [Conditional Expression 9] 0< f6/f [Conditional Expression 10] f7/f < 0 [Conditional Expression 11]OAL/f < 1.4 [Conditional Expression 12] −1.3 < f1/f2 [ConditionalExpression 13] −2.0 < f2/f3 < 0 [Conditional Expression 14] BFL/f < 0.4[Conditional Expression 15] D2/f < 0.1 [Conditional Expression 16] 80 <FOV [Conditional Expression 17] F No. ≤ 2.05

In the Conditional Expressions, f represents an overall focal length ofthe optical imaging system, f1 represents a focal length of the firstlens, f2 represents a focal length of the second lens, f3 represents afocal length of the third lens, f4 represents a focal length of thefourth lens, f5 represents a focal length of the fifth lens, f6represents a focal length of the sixth lens, f7 represents a focallength of the seventh lens, V1 represents an Abbe number of the firstlens, V2 represents an Abbe number of the second lens, V3 represents anAbbe number of the third lens, and V5 represents an Abbe number of thefifth lens. In addition, OAL represents a distance from an object-sidesurface of the first lens to an imaging plane, BFL represents a distancefrom an image-side surface of the seventh lens to an imaging plane, andD2 represents a distance from an image-side surface of the first lens toan object-side surface of the second lens.

Conditional Expression 1 is a relational expression for limiting therefractive power of the first lens. In a case when the first lens isoutside of the numerical range of Conditional Expression 1, refractivepower distribution of different lenses may be limited.

Conditional Expressions 2 through 4 are relational expressions forimproving chromatic aberration of an optical imaging system. Forexample, improvement of chromatic aberration of an optical imagingsystem may be limited in cases outside of the numerical ranges ofConditional Expressions 2 through 4.

Conditional Expressions 5 through 7 are relational expressions forimproving aberration correction of an optical imaging system. Forexample, aberration correction in optical imaging systems outside of thenumerical ranges of Conditional Expressions 5 through 7 are limited,because refractive power of the second lens to the fourth lens issignificantly high or low.

Conditional Expressions 8 through 10 are relational expressions forlimiting the refractive power of an imaging optical system. For example,maintaining a desired refractive power of the fifth lens to the seventhlens is limited in cases outside of the numerical ranges of ConditionalExpressions 8 through 10.

Conditional Expressions 11 and 14 are relational expressions forminiaturization of the optical imaging system. For example, in opticalimaging systems outside of the numerical ranges of ConditionalExpressions 11 and 14, a distance from the first lens to an imagingplane is significantly long. Thus, the optical imaging system cannot besufficiently miniaturized.

Conditional Expressions 12 and 13 are relational expressions forimproving aberration characteristics of the optical imaging system. Forexample, in optical imaging systems outside of the numerical ranges ofConditional Expressions 12 and 13, a refractive power of a specific lensof the first lens to the third lens is significantly large. Thus,aberration characteristics may deteriorate. Conditional Expression 15 isalso a relational expression for improving aberration characteristics ofan optical imaging system. For example, improvement to longitudinalchromatic aberration of an optical imaging system is limited in casesoutside of an upper limit value of Conditional Expression 15.

The optical imaging system satisfying Conditional Expressions describedabove may obtain a bright image. For example, the optical imaging systemmay have an F number of 2.05 or less. In addition, the optical imagingsystem may implement a resolution of 13 megapixels or more, and may havea wide angle of view of 80 degrees or more.

Next, optical imaging systems, according to several examples, will bedescribed. First, an optical imaging system, according to a firstexample, will be described with reference to FIG. 1. An optical imagingsystem 100 includes a first lens 110, a second lens 120, a third lens130, a fourth lens 140, a fifth lens 150, a sixth lens 160, and aseventh lens 170.

The first lens 110 has a positive refractive power. An object-sidesurface of lens 110 is convex, and an image-side surface of lens 110 isconcave. The second lens 120 has a negative refractive power. Anobject-side surface of lens 120 is convex, and an image-side surface oflens 120 is concave. The third lens 130 has a positive refractive power.An object-side surface of lens 130 is convex, and an image-side surfaceof lens 130 is concave. The fourth lens 140 has a positive refractivepower. An object-side surface of lens 140 is concave, and an image-sidesurface of lens 140 is convex.

The fifth lens 150 has a negative refractive power. An object-sidesurface of lens 150 is concave, and an image-side surface of lens 150 isconvex. The sixth lens 160 has a positive refractive power. Anobject-side surface of lens 160 is convex, and an image-side surface oflens 160 is concave. In addition, the sixth lens 160 has an inflectionpoint formed on both of its surfaces. The seventh lens 170 has anegative refractive power. An object-side surface of lens 170 is convex,and an image-side surface of lens 170 is concave. In addition, theseventh lens 170 has an inflection point formed on both of its surfaces.

Optical imaging system 100 further includes a filter 180, an imagesensor 190, and a stop ST. Filter 180 may be disposed between seventhlens 170 and image sensor 190. Stop ST may be disposed between secondlens 120 and third lens 130 or between third lens 130 and fourth lens140.

The optical imaging system configured as described above representsaberration characteristics as illustrated by the graphs shown in FIG. 2.FIG. 3 lists aspherical characteristics of the optical imaging system,according to the first example. Lens characteristics of the opticalimaging system, according to the first example, are described in Table1.

TABLE 1 First Example FOV = 81.9 F No = 2.00 f = 3.671 OAL = 4.200Number of Radius of Thickness/ Refractive Abbe Focal surface curvatureDistance index number length S1 First lens 1.3225 0.5006 1.547 56.1003.284 S2 4.3551 0.0200 S3 Second lens 3.5653 0.1500 1.669 20.350 −8.740S4 2.1771 0.1624 S5 Third lens 3.1365 0.2284 1.547 56.100 13.548 S65.3019 0.2563 S7 Fourth lens −13.3504 0.2620 1.547 56.100 75.065 S8−10.1423 0.2108 S9 Fifth lens −3.9034 0.2300 1.658 21.494 −13.184 S10−7.2623 0.1660 S11 3.0156 0.3939 1.658 21.494 44.153 S12 Sixth lens3.1904 0.2101 S13 Seventh lens 1.6112 0.4621 1.537 55.700 −17.987 S141.2425 0.1961 S15 Filter Infinity 0.1100 1.519 64.197 S16 Infinity0.6410 S18 Imaging plane Infinity 0.0000

With reference to FIG. 4, an optical imaging system, according to asecond example, will be described. An optical imaging system 200includes a first lens 210, a second lens 220, a third lens 230, a fourthlens 240, a fifth lens 250, a sixth lens 260, and a seventh lens 270.

The first lens 210 has a positive refractive power. An object-sidesurface of lens 210 is convex, and an image-side surface of lens 210 isconcave. The second lens 220 has a negative refractive power. Anobject-side surface of lens 220 is convex, and an image-side surface oflens 220 is concave. The third lens 230 has a positive refractive power.An object-side surface of lens 230 is convex, and an image-side surfaceof lens 230 is concave. The fourth lens 240 has a positive refractivepower. An object-side surface of lens 240 is concave, and an image-sidesurface of lens 240 is convex.

The fifth lens 250 has a negative refractive power. An object-sidesurface of lens 250 is concave, and an image-side surface of lens 250 isconvex. The sixth lens 260 has a positive refractive power. Anobject-side surface of lens 260 is convex, and an image-side surface oflens 260 is concave. In addition, the sixth lens 260 has an inflectionpoint formed on both of its surfaces. The seventh lens 270 has anegative refractive power. An object-side surface of lens 270 is convex,and an image-side surface of lens 270 is concave. In addition, theseventh lens 270 has an inflection point formed on both of its surfaces.

Optical imaging system 200 further includes a filter 280, an imagesensor 290, and a stop ST. Filter 280 may be disposed between seventhlens 270 and image sensor 290 Stop ST may be disposed between secondlens 220 and third lens 230 or between third lens 230 and fourth lens240.

The optical imaging system configured as described above representsaberration characteristics as illustrated by the graphs shown in FIG. 5.FIG. 6 lists aspherical characteristics of the optical imaging system,according to the second example. Lens characteristics of the opticalimaging system, according to the second example, are described in Table2.

TABLE 2 Second Example FOV = 81.8 F No = 2.05 f = 3.685 OAL = 4.200Number of Radius of Thickness/ Refractive Abbe Focal surface curvatureDistance index number length S1 First lens 1.3038 0.4873 1.547 56.1003.293 S2 4.1066 0.0200 S3 Second lens 3.1322 0.1500 1.669 20.350 −8.705S4 1.9973 0.1652 S5 Third lens 3.1435 0.2270 1.547 56.100 14.115 S65.1702 0.2384 S7 Fourth lens −18.6194 0.2513 1.547 56.100 90.636 S8−13.5970 0.2428 S9 Fifth lens −3.8728 0.2300 1.658 21.494 −15.266 S10−6.4514 0.1738 S11 Sixth lens 3.3763 0.3820 1.658 21.494 40.265 S123.6956 0.2187 S13 Seventh lens 1.6490 0.4759 1.537 55.700 −15.456 S141.2370 0.1961 S15 Filter Infinity 0.1100 1.519 64.197 S16 Infinity0.6320 S18 Imaging plane Infinity 0.0000

With reference to FIG. 7, an optical imaging system, according to athird example, will be described. An optical imaging system 300 includesa first lens 310, a second lens 320, a third lens 330, a fourth lens340, a fifth lens 350, a sixth lens 360, and a seventh lens 370.

The first lens 310 has a positive refractive power. An object-sidesurface of lens 310 is convex, and an image-side surface of lens 310 isconcave. The second lens 320 has a negative refractive power. Anobject-side surface of lens 320 is convex, and an image-side surface oflens 320 is concave. The third lens 330 has a positive refractive power.An object-side surface of lens 330 is convex, and an image-side surfaceof lens 330 is concave. The fourth lens 340 has a positive refractivepower. An object-side surface of lens 340 is concave, and an image-sidesurface of lens 340 is convex.

The fifth lens 350 has a negative refractive power. An object-sidesurface of lens 350 is concave, and an image-side surface of lens 350 isconvex. The sixth lens 360 has a positive refractive power. Anobject-side surface of lens 360 is convex, and an image-side surface oflens 360 is concave. In addition, the sixth lens 360 has an inflectionpoint formed on both of its surfaces. The seventh lens 370 has anegative refractive power. An object-side surface of lens 370 is convex,and an image-side surface of lens 370 is concave. In addition, theseventh lens 370 has an inflection point formed on both of its surfaces.

Optical imaging system 300 further includes a filter 380, an imagesensor 390, and a stop ST. Filter 380 may be disposed between seventhlens 370 and image sensor 390. Stop ST may be disposed between secondlens 320 and third lens 330 or between third lens 330 and fourth lens340.

The optical imaging system configured as described above representsaberration characteristics as illustrated by the graphs shown in FIG. 8.FIG. 9 lists aspherical characteristics of the optical imaging system,according to the third example. Lens characteristics of the opticalimaging system, according to the third example, are described in Table3.

TABLE 3 Third Example FOV = 82.1 F No = 1.99 f = 3.661 OAL = 4.200Number of Radius of Thickness/ Refractive Abbe Focal surface curvatureDistance index number length S1 First lens 1.3218 0.4999 1.547 56.1003.280 S2 4.3592 0.0200 S3 Second lens 3.5574 0.1500 1.669 20.350 −8.812S4 2.1808 0.1605 S5 Third lens 3.1908 0.2251 1.547 56.100 14.304 S65.2570 0.2445 S7 Fourth lens −19.3465 0.2575 1.547 56.100 88.905 S8−13.9019 0.2233 S9 Fifth lens −3.9145 0.2300 1.658 21.494 −14.053 S10−6.9465 0.1659 S11 Sixth lens 3.1391 0.3975 1.658 21.494 45.800 S123.3280 0.2000 S13 Seventh lens 1.6131 0.4733 1.537 55.700 −19.470 S141.2542 0.1961 S15 Filter Infinity 0.1100 1.519 64.197 S16 Infinity0.6460 S18 Imaging plane Infinity 0.0000

Table 4 represents a conditional expression value of the optical imagingsystem, according to the first example to the third example.

TABLE 4 Conditional First Second Third Expression Example ExampleExample f1/f 0.894 0.894 0.896 V1 − V2 35.75 35.75 35.75 V1 − V3 0.000.00 0.00 V1 − V5 34.606 34.606 34.606 f2/f −2.380 −2.362 −2.407 f3/f3.690 3.830 3.907 |f4/f| 20.446 24.597 24.283 f5/f −3.591 −4.143 −3.838f6/f 12.026 10.927 12.510 f7/f −4.899 −4.195 −5.318 OAL/f 1.144 1.1401.147 f1/f2 −0.376 −0.378 −0.372 f2/f3 −0.645 −0.617 −0.616 BFL/f 0.2580.255 0.260 D2/f 0.005 0.005 0.005

As set forth above, according to examples, an optical imaging systemcapable of long distance imaging, while being mounted in a smallterminal, may be implemented. While this disclosure includes specificexamples, it will be apparent after an understanding of the disclosureof this application that various changes in form and details may be madein these examples without departing from the spirit and scope of theclaims and their equivalents. The examples described herein are to beconsidered in a descriptive sense only, and not for purposes oflimitation. Descriptions of features or aspects in each example are tobe considered as being applicable to similar features or aspects inother examples. Suitable results may be achieved if the describedtechniques are performed in a different order, and/or if components in adescribed system, architecture, device, or circuit are combined in adifferent manner, and/or replaced or supplemented by other components ortheir equivalents. Therefore, the scope of the disclosure is defined notby the detailed description, but by the claims and their equivalents,and all variations within the scope of the claims and their equivalentsare to be construed as being included in the disclosure.

What is claimed is:
 1. An optical imaging system, comprising: a firstlens comprising a concave image-side surface along an optical axis; asecond lens comprising a concave image-side surface along the opticalaxis; a third lens comprising a positive refractive power; a fourth lenscomprising a positive refractive power and a concave object-side surfacealong the optical axis; a fifth lens; a sixth lens comprising a positiverefractive power; and a seventh lens comprising a convex object-sidesurface along the optical axis, wherein the first lens to the seventhlens are sequentially disposed from an object side toward an imagingplane.
 2. The optical imaging system of claim 1, wherein an object-sidesurface of the first lens is convex along the optical axis.
 3. Theoptical imaging system of claim 1, wherein an object-side surface of thesecond lens is convex along the optical axis.
 4. The optical imagingsystem of claim 1, wherein an object-side surface of the third lens isconvex along the optical axis.
 5. The optical imaging system of claim 1,wherein an image-side surface of the third lens is concave along theoptical axis.
 6. The optical imaging system of claim 1, wherein anobject-side surface of the fifth lens is concave along the optical axis.7. The optical imaging system of claim 1, wherein an image-side surfaceof the fifth lens is convex along the optical axis.
 8. The opticalimaging system of claim 1, wherein an object-side surface of the sixthlens is convex along the optical axis.
 9. The optical imaging system ofclaim 1, wherein an image-side surface of the sixth lens is concavealong the optical axis.
 10. The optical imaging system of claim 1,wherein an image-side surface of the seventh lens is concave along theoptical axis.
 11. An optical imaging system, comprising: a first lens, asecond lens, a third lens, a fourth lens, a fifth lens, a sixth lens,and a seventh lens, sequentially disposed from an object side toward animaging plane, wherein the optical imaging system satisfies thefollowing Conditional Expression:f2/f<−2.0 where f represents an overall focal length of the opticalimaging system and f2 is a focal length of the second lens.
 12. Theoptical imaging system of claim 11, wherein the optical imaging systemsatisfies the following Conditional Expression:0<f1/f<2.0 where f1 represents a focal length of the first lens.
 13. Theoptical imaging system of claim 11, wherein the optical imaging systemsatisfies the following Conditional Expressions:25<V1−V2<45,V1−V3<25, and25<V1−V5<45 where V1 represents an Abbe number of the first lens, V2represents an Abbe number of the second lens, V3 represents an Abbenumber of the third lens, and V5 represents an Abbe number of the fifthlens.
 14. The optical imaging system of claim 11, wherein the opticalimaging system satisfies the following Conditional Expression:1.5<f3/f where f3 represents a focal length of the third lens.
 15. Theoptical imaging system of claim 11, wherein the optical imaging systemsatisfies the following Conditional Expression:3.0<|f4/f| where f4 represents a focal length of the fourth lens. 16.The optical imaging system of claim 11, wherein image-side surfaces ofthe first lens and the sixth lens are concave, and an object-sidesurface of the fourth lens is concave.